Liquid crystal displays are generally formed of two panels, each having a transparent electrode pattern. The function of the pattern on the panels is to apply an electrical field across a liquid crystal fluid residing in a gap between the panels, thereby causing a change in the optical properties of the liquid crystal. One or both of the panels is typically transparent in order that a change in the liquid crystal might be viewed by a user. Each panel is connected to a suitable voltage source. The voltage source powers the elements that have been patterned on one or both of the panels in order to provide the display, with the elements of pattern in a shape corresponding to the information that is to be displayed. For example, the pattern may represent the outline of a variety of letters, numbers, or symbols.
The elements in the pattern typically are formed from a material such as indium-tin oxide (ITO). The elements are then connected to the voltage source by a conductive metal bus system. These electrodes are usually prepared by first coating one surface of a substrate by vacuum deposition of the ITO. Portions of the ITO are then selectively removed by etching in order to produce the desired electrode pattern. In order to confine the etching to selected areas, the ITO layer is covered with a photoresist or layer of photopolymerizable material. The photoresist is then polymerized in the desired image by exposure to radiation, such as ultraviolet light. The unpolymerized resist in the unexposed area is then removed by a suitable solvent in order to form windows in the resist. The uncovered areas of the ITO layer are then etched away with appropriate solvents such as acids, in order to create the pattern. The remaining portions of the photoresist layer are then stripped off, leaving the substrate with the desired electrode pattern formed thereon.
While this method of photoetching patterns makes it possible to prepare very complex patterns having very fine lines, aggressive acids are required to etch the ITO. These acids can attack some substrates, such as plastics. Prior art solutions to avoid this problem have included lift-off methods in which a photoresist is applied and imaged directly on the substrate. The metal film is then deposited on the resist and the substrate, and when the resist is stripped away, it takes the unwanted portions of the metal film with it. Conductor resolution is defined solely by the lithography of the resist. One problem with conventional lift-off techniques is that they use aggressive stripping solutions to remove the polymerized resist, which may be harmful to plastic substrates used in flexible displays.
Therefore, a need has continued to exist for a method of producing electrode patterns on a substrate which avoid the problems introduced by known and conventional methods of the art.